1. Field of the Invention
The present invention relates to a semiconductor device that includes a cell region in which a semiconductor element is disposed and a peripheral region surrounding the cell region and having a high breakdown voltage structure.
2. Description of the Related Art
JP-A-11-74524 (corresponding to U.S. Pat. No. 6,054,752) and JP-A-2007-165604 (corresponding to U.S. Pat. No. 2009/0045413 A1) disclose high breakdown voltage structures formed in a peripheral region surrounding a cell region in which a semiconductor element such as a vertical power MOSFET and a diode is formed. FIG. 13 is a cross-sectional view of a high breakdown voltage structure formed in a peripheral region of a semiconductor device disclosed in JP-A-11-74524.
As shown in FIG. 13, the semiconductor device includes an n type drift layer 101, a p type layer 102 disposed on the n type drift layer 101, a recess section 103, and an electric field relaxing layer 104 having a p type. The recess section 103 forms a mesa structure and the electric field relaxing layer 104 is disposed on a sidewall and a bottom of the mesa structure. The recess section 103 for forming the mesa structure is provided from the p type layer 102 into the n type drift layer 101. At a stepped portion of the mesa structure, the electric field relaxing layer 104 is disposed from a surface of the p type layer 102 to a surface of the n type drift layer 101 in the recess section 103. By forming the electric field relaxing layer 104, equipotential lines gently extend toward a peripheral region, and an electric field concentration is relaxed. Thus, a breakdown voltage can be improved.
The high breakdown voltage structures disclosed in JP-A-11-74524 and JP-A-2007-165604 have a discontinuous point where materials having different conductivity types are connect with each other at a portion being in contact with the electric field relaxing layer and a bending portion at which an electric field relaxing layer is bent. For example, in the high breakdown voltage structure disclosed in JP-A-11-74524, a discontinuous point where an n type semiconductor connects with a p type semiconductor is located at a region R1 in FIG. 13, and a bending portion of the electric field relaxing layer is located at a region R2 in FIG. 13. Thus, the electric field may concentrate at the regions R1 and R2, and the breakdown voltage may be reduced.